EP0937210 shows a brake adjuster mechanism for a disc brake. The brake adjuster mechanism includes a torque limiting clutch and a one-way clutch. When the brake is applied a gear segment rotates one part of a torque limiting clutch. At relatively low torque (i.e. at torques below the limiting torque of the clutch) rotation of the first part will cause rotation of the second part which in turn drives an adjuster gear of the brake via the one-way clutch. The adjuster gear adjusts the brake mechanism so as to compensate for wear of the brake pads. If no wear adjustment is required, the limiting torque will be exceeded and ball elements of the torque limiting clutch will be forced out of associated pockets thereby enabling the first part to rotate relative to the second part when the limiting torque is exceeded. Upon release of the brake the first part is rotated backwards and the ball elements returned to their original pockets and the torque limiting clutch returns to its original position. The one way clutch ensures that the adjuster gear remains in its adjusted position. Thus, upon substantially every application of the brake the torque limiting clutch will exceed its torque limit and therefore the components of the adjuster mechanism will be subjected to a torque equivalent to the torque limit. This causes wear of the adjuster components.
EP0963520 shows an alternative arrangement whereby a gear segment drives a torque limiting clutch which in turn drives an adjuster gear via a one-way clutch. The components of this mechanism are subject to the limiting clutch torque upon substantially every application of the brake, which leads to wear.
Typically, when a brake disc is not being applied there will be a running clearance between each brake pad and the disc. For a heavy vehicle this running clearance is of the order of 0.5 mm between each pad and the disc, i.e. a total of the order of 1 mm from the brake assembly as a whole. The running clearance is determined by the backlash in the adjuster mechanism. The adjuster mechanism is therefore designed with a predetermined amount of backlash, equivalent to the required running clearance of the brake. As the components of the adjuster mechanism wear, then so the backlash in the adjuster mechanism increases which results in an increase in the running clearance of the brake. This is undesirable.
Thus, an improved form of brake adjuster is required which is subject to less wear.